Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 qemu-img.texi | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/qemu-img.texi b/qemu-img.texi
index 60a0e080c6..e83e140f7a 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -86,6 +86,15 @@ exclusive with the @var{-O} parameters. It is currently required to also use
 the @var{-n} parameter to skip image creation. This restriction may be relaxed
 in a future release.
 
+@item --force-share (-U)
+
+If specified, @code{qemu-img} will open the image with shared permissions,
+which makes it less likely to conflict with a running guest's permissions due
+to image locking. For example, this can be used to get the image information
+(with 'info' subcommand) when the image is used by a running guest. Note that
+this could produce inconsistent results because of concurrent metadata changes,
+etc. This option is only allowed when opening images in read-only mode.
+
 @item --backing-chain
 will enumerate information about backing files in a disk image chain. Refer
 below for further description.
-- 
2.14.3

On 2017-12-26 03:52, Fam Zheng wrote:
> Signed-off-by: Fam Zheng <famz@redhat.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  qemu-img.texi | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/qemu-img.texi b/qemu-img.texi
> index 60a0e080c6..e83e140f7a 100644
> --- a/qemu-img.texi
> +++ b/qemu-img.texi
> @@ -86,6 +86,15 @@ exclusive with the @var{-O} parameters. It is currently required to also use
>  the @var{-n} parameter to skip image creation. This restriction may be relaxed
>  in a future release.
>  
> +@item --force-share (-U)
> +

So the previous patch makes the use of blank lines consistent and this
one breaks it again? :-)

> +If specified, @code{qemu-img} will open the image with shared permissions,
> +which makes it less likely to conflict with a running guest's permissions due
> +to image locking. For example, this can be used to get the image information
> +(with 'info' subcommand) when the image is used by a running guest. Note that
> +this could produce inconsistent results because of concurrent metadata changes,
> +etc. This option is only allowed when opening images in read-only mode.

I personally don't quite like the "makes it less likely to conflict",
because that makes it sound like qemu would be stupid and need a nudge
in the right direction -- when it's actually the user who does something
a bit risky (and qemu is right in forbidding it by default).  But since
it's only a read-only thing, I won't actually object to it.

(Maybe it should document more exactly what's happening, i.e. that this
option will allow concurrent writers (as a standard user, I wouldn't
know what "shared permissions" is supposed to mean).)

Max

> +
>  @item --backing-chain
>  will enumerate information about backing files in a disk image chain. Refer
>  below for further description.
> 

On Mon, Jan 29, 2018 at 05:01:41PM +0100, Max Reitz wrote:
> On 2017-12-26 03:52, Fam Zheng wrote:

[...]

> So the previous patch makes the use of blank lines consistent and this
> one breaks it again? :-)
> 
> > +If specified, @code{qemu-img} will open the image with shared permissions,
> > +which makes it less likely to conflict with a running guest's permissions due
> > +to image locking. For example, this can be used to get the image information
> > +(with 'info' subcommand) when the image is used by a running guest. Note that
> > +this could produce inconsistent results because of concurrent metadata changes,
> > +etc. This option is only allowed when opening images in read-only mode.
> 
> I personally don't quite like the "makes it less likely to conflict",
> because that makes it sound like qemu would be stupid and need a nudge
> in the right direction -- when it's actually the user who does something
> a bit risky (and qemu is right in forbidding it by default).  But since
> it's only a read-only thing, I won't actually object to it.
> 
> (Maybe it should document more exactly what's happening, i.e. that this
> option will allow concurrent writers (as a standard user, I wouldn't
> know what "shared permissions" is supposed to mean).)

Eerie -- Although I reviewed it, I was just mulling over this wording
yesterday (while I was tweaking the wording of '--force-share' on a
slide for a public conference).  

Indeed, "concurrent writers" is much clearer.


[...]


-- 
/kashyap

On Tue, Jan 30, 2018 at 12:01 AM, Max Reitz <mreitz@redhat.com> wrote:
> On 2017-12-26 03:52, Fam Zheng wrote:
>> Signed-off-by: Fam Zheng <famz@redhat.com>
>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>> Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>
>> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
>> ---
>>  qemu-img.texi | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/qemu-img.texi b/qemu-img.texi
>> index 60a0e080c6..e83e140f7a 100644
>> --- a/qemu-img.texi
>> +++ b/qemu-img.texi
>> @@ -86,6 +86,15 @@ exclusive with the @var{-O} parameters. It is currently required to also use
>>  the @var{-n} parameter to skip image creation. This restriction may be relaxed
>>  in a future release.
>>
>> +@item --force-share (-U)
>> +
>
> So the previous patch makes the use of blank lines consistent and this
> one breaks it again? :-)

Good point, will fix.

>
>> +If specified, @code{qemu-img} will open the image with shared permissions,
>> +which makes it less likely to conflict with a running guest's permissions due
>> +to image locking. For example, this can be used to get the image information
>> +(with 'info' subcommand) when the image is used by a running guest. Note that
>> +this could produce inconsistent results because of concurrent metadata changes,
>> +etc. This option is only allowed when opening images in read-only mode.
>
> I personally don't quite like the "makes it less likely to conflict",
> because that makes it sound like qemu would be stupid and need a nudge
> in the right direction -- when it's actually the user who does something
> a bit risky (and qemu is right in forbidding it by default).  But since
> it's only a read-only thing, I won't actually object to it.
>
> (Maybe it should document more exactly what's happening, i.e. that this
> option will allow concurrent writers (as a standard user, I wouldn't
> know what "shared permissions" is supposed to mean).)

Makes sense to me. Sending v6.

Fam